title: Mycobacterial factors relevant for transmission of tuberculosis.
abstract: BACKGROUND
  Tuberculosis (TB) transmission is associated with patient-related risk factors. However, DNA fingerprint analysis has provided anecdotal evidence suggesting a role for bacteriological factors.
  
  
  METHODS
  To examine the importance of the bacteriological component in TB transmission, we investigated the number of tuberculin skin test-positive (TST induration, ≥ 10 mm) contacts and secondary cases observed in contact investigations around TB cases in relation to the size of the genotype cluster the patient belonged to at the time of diagnosis. We also compared the number of TST-positive contacts and secondary cases of patients with drug-resistant and drug-susceptible TB.
  
  
  RESULTS
  Larger clusters were independently associated with an increased number of positive contacts. The mean number of positive contacts ranged from 3.8 for clusters of 2 cases, to 4.7 for clusters of 3-10 cases, to 6.0 for cases in clusters of >10 cases (mean increase in number of positive contacts for every extra case in the cluster, 0.21; 95% confidence interval, 0.09-0.26). The mean number of positive contacts was significantly lower among index cases with isoniazid-monoresistant TB (1.6) than among index cases with pan-susceptible TB (4.6; relative number, 0.45; 95% confidence interval, 0.22-0.92).
  
  
  CONCLUSIONS
  These results suggest that spread of tuberculosis also depends on bacteriological factors.
authors.affiliation: Tuberculosis Reference Laboratory, Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven. lillyverhagen@hotmail.com
authors.forename: Lilly M
authors.initials: LM
authors.lastname: Verhagen
authors.forename: Susan
authors.initials: S
authors.lastname: van den Hof
authors.forename: Henk
authors.initials: H
authors.lastname: van Deutekom
authors.forename: Peter W M
authors.initials: PW
authors.lastname: Hermans
authors.forename: Kristin
authors.initials: K
authors.lastname: Kremer
authors.forename: Martien W
authors.initials: MW
authors.lastname: Borgdorff
authors.forename: Dick
authors.initials: D
authors.lastname: van Soolingen
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015373:Bacterial Typing Techniques; D016000:Cluster Analysis; D016358:Contact Tracing; D016172:DNA Fingerprinting; D004269:DNA, Bacterial / Q000235:genetics; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D058889:Molecular Typing; D009169:Mycobacterium tuberculosis / Q000145:classification / Q000235:genetics* / Q000472:pathogenicity*; D014374:Tuberculin Test; D014376:Tuberculosis / Q000382:microbiology* / Q000635:transmission*; D037521:Virulence Factors / Q000235:genetics
chemical_list: D004269:DNA, Bacterial; D037521:Virulence Factors